Prevention of corrosion of structural metals by hydrogen sulfide, air, and water



Patented Oct. 16, 1951 PREVENTION OF CORROSION OF STRUC- TURALv METALS BY HYDROGEN SUL- FIDE, AIR, AND WATER Glenn A. Marsh, Crystal Lake, 111., asslgnor to The Pure Oil Company, Chicago, 111., a corporation of Ohio NoDrawing. Application October 28, 1949,

Serial No. 124,240

8 Claims. (Cl. 21-2-5) typified by the West Texas fields has resulted in numerous production, processing and storage problems occasioned by the high hydrogen sulfide content of the produced crude oil. Due to the high hydrogen sulfide content of these crude oils, with its accompanying disadvantages, these and like crude oils have been termed sour crudes. Hereinafter, any illusion to such crude oils will be made by referring to them by the above expression, viz., sour crudes. Before these sour crudes may be effectively utilized there are many disadvantagous effects which have to be overcome, the major disadvantage being in the corresive properties inherent in said crudes. The corrosive conditions effected by the presence of these sour crudes have to be remedied in a manner generally peculiar to each handling and processing situation. The prior art has disclosed many efforts of investigators in combating the deleterious effects of these various and different hydro gen sulfide-containing corrosive environments.

Mechanical procedures have been used with some degree of success. These include cladding or strip-lining the metal surface exposed to the corrosive environment with a corrosion-resistant metal typified by chrome-nickel or chromenickel-molybdenum alloy steels. This type of protection has been confined in the main to process vessels operating under pressure and to process piping. Heater tubes in said corrosive service are frequently fabricated entirely from the corrosive resistant alloy instead of being merely lined with a corrosion resistant metal on the exposed surfaces. Other mechanical means have been applied to the exposed surfaces of storage tanks to protect themfrom corrosion. These consist in applying a protective coating of a plastic type composition avin a bituminous or synthetic resin base to the metal surface in order to prevent this metal surface from being contacted by the corrosive atmosphere. The spraying and consequent coating of the exposed metal surfaces of storage tanks with a cementitious composition has also been widely used to protect the metal surfaces from corrosion.

The prevention of corrosion, of metals by certain hydrogen sulfide-containing systems, by chemical means has also been investigated. Menaul in United States Patent 2,426,318, shows the prevention of corrosion of metallic surfaces exposed to hydrogen sulfide-brine systems encountered ln the production of sour crude oils by injecting formaldehyde into the bore hole during the production stage. The use of pyridine or quinoline to inhibit the corrosion of a similar environment is taught in United States Patent 2,472,400.

It is an object of the present invention, therefore, to provide a chemical method for inhibiting the corrosion of metal surfaces caused by the corrosive action of systems containing hydrogen sulfide, air and water. Another object is to provide a method for the inhibition of the chemical attack on metal surfaces exposed to a confined, corrosive atmosphere consisting essentially of hydrogen sulfide, air and water by introducing a palliative into the confined space. A still further object is carried out in the storage of a sour i crude oil in which the corrosion of the vapor space above the crude oil is mitigated by the addition'of an inhibition agent into the said vapor space. 7

According to the present invention, we have found a method of melioratlng the corrosive effects of a hydrogen sulfide, air and water-containing system on a metal by introducing another component into the system. This added component is in the form of a low molecular weight alpha, beta-unsaturated aldehyde, particularly crotonaldehyde.

One embodiment of this invention consists in introducing a low molecular weight alpha, betaunsaturated aldehyde, particularly crotonaldehyde, into the vapor space over a fluid which provides the hydrogen sulfide component of corrosive hydrogen sulfide, water and air-containing system.

A more specific embodiment is found in the inhibition of corrosion of the metal structure of storage tanks used in sour crude oil service by introducing a low molecular weight alpha, betaunsaturated aldehyde, particularly crotonaldehyde, into the vapor space occurring over the sour crude oil.

In carrying out the invention, various methods of introducing the said aldehyde into the vapor space maybe used. A specific method is taught in principle by United states Patent 1,930,592. An adaptation of this principle to the instant invention would consist-in appending a reservoir containing our corrosion inhibition agent to the breathing vent of the storage tank. The corrosion inhibitor is so disposed within said reservoir that when air is drawn through the said reservoir toward the vapor space of the tank it necessarily passes in gas-liquid contact with the inhibitor. The air is thereby partially saturated with the inhibitor and carries 'it into the vapor space. We have found that the amount of said aldehyde added to the vapor space by this procedure will usually suflice to inhibit the corrosive atmosphere present under such conditions. In order, however. to combat extreme conditions which are not readily remedied by this particular installation means can be provided for the independent injection of additional amounts of aldehyde in order to provide a suflicient concentration of aldehyde necessary for proper inhibition. It is evident that, up to a certain extent, the greater the concentration or said aldehyde vapor present in the confined corrosive medium, the more efiective is the inhibition of corrosion. We have found, however, that no practical advantage is .to be obtained in exceeding vapor concentrationsof over about volume per cent. Other methods of application are possible and should be apparent to those carrying out the teachings of the invention.

While certain phases of the investigation of the behavior of these low molecular weight alpha, beta-unsaturated aldehydes and other possible inhibitors for hydrogen sulfide-air-water corrosion were carried out under conditions prevailing in sour crude storage facilities, they are shownonly for the purposes of illustration. These particular experiments should not be construed in such a manner that would lead one to believe that the invention is confined to this specific application. In order that the effect on corrosion rate produced by the various possible inhibitors tested could be studied the following experimental 'procedures were developed:

(1) CORROSION TESTS USING SOXHLET EXTRACTION APPARATUS A weighed mild steel coupon was suspended in the extraction chamber of a Soxhlet extraction apparatus. Water boiling at a controlled rate in a flask below the extractor caused the chamber to fill with water and empty at spaced intervals causing alternate immersion with subsequent drying of the metal surface. Water containing a mixture of 50% air-50% hydrogen sulfide, said mixture being water-saturated at 70 F., was passed over the coupon at a rate of three (3) liters per hour. In all instances except the blank run, the air-hydrogen sulfide mixture was bubbled through cc. of the inhibitor being tested. This procedure provided for the substantial saturation of the gaseous mixture with the respective inhibitor being used. Each run was carried out under similar conditions of time and temperature. After completion of a run. the test coupons were removed from the apparatus and pickled in sulfuric acid to remove the corrosion products. Subsequent treatment consisted in washing, drying and weighing the coupon. -Results of this test are given in Table I.

TABLE I Results of corrosion tests using Soxhlet extractraction apparatus Wei ht Per cent No. Inhibitor Lo s, Inhibi- Mg 1 tion I None 2 .4 Fornzlaldehyde 35.6 --4 1 Isoquinoline. 23.5 11 Acrolein 8.4 71 Crotonaldehyde 3. 2 89 Furlural 20.3 28 N -'Iolusldehyde 25. 3 8 Cinnamaldehyde l5. 5 43 l A weight loss 01' 10 mg. corresponds to a uniform rate of 6.0076 inch penetration per year.

(2) STATIC TESTS A weighed coupon of mild steelwas suspended and 1 volume per cent, based on the flask volume, of liquid inhibitor contained in an opentop vial was placed in the flask. The flasks were sealed with the aforementioned rubber stoppers and allowed to stand at room temperature for about 10 days. At the end of this time, the coupons were cleaned by pickling with sulfuric acid,

dried and weighed. Results obtained by this procedure are. shown in Table II.

TABLE II Results of static tests on vapor phase inhibitors Wei ht Dur t P No. Inhibitor Lo s, 0? Ion Isl ri Mg. Test tion Da .1 None 315 '10 0 Crotonaldehyde 58 10 1 82 Isopropyl amine nitrate-.. 118 10 62 None 128 9.5 0 Crotonaldehyde 19 9. 5 85 p-ethoxyethylam' 86 9. 5 33 ethylene diamine 230 9. 5 -&l

SIMULATED soon. CRUDE on.

STORAGE TESTS 'In order'to simulate the conditions in the vapor space of sour crude oil storage tanks, 8. test was devised using cans having friction fitted removable lids. The tests were carried out by providing a polishedsurfaceon a previously unused can lid by appropriate treatment of a selected area of the can lid inner surface. The cans were partially filled with hydrogen sulfide saturated crude. Means for providing a high relative humidity .of the confined vapor space was disposed inside the can. In all instancesexcept where a blank run was being conducted, a. beaker containing the inhibitor being tested was placed in the can. The can was sealed by securely fitting the lid to the can opening. The test assemblies were exposed to the atmospheric weather conditions prevailing during the tests. More severe conditions were artificially produced by additional indoor tests. After an exposure of several weeks sulfur and hydrated iron oxide. In this action. the extreme influence of oxygen on corrosion, such as through formation of concentration cel s. is reduced and pitting is therefore reduced. While to selected conditions, either naturally occurring the application of this theory has been directed or artificially produced and during which time specifically to crotonaldehyde, it is evident that the oil inthe cans was changed periodically to other low molecular weight'condugated aldehydes. insure an adequate concentration of hydrogen such as acrolein, are reasonably effective as simsulflde, the lids were removed by pickling with ilar corrosion inhibition agents. inhibited sulfuric acid. After washing and drv- The preferred embodiment of this invention is ing, the lids were again weighed. Table III is in its application to the melioration of the corprovided to indicate the experimental results rosion problems present in the .vapor space of obtained in this series of tests. sour crude oil storage tanks but it is by no means TABLE III Simulated crude oil storage tests Exposure Conditions No Inhibitor Present Inhibitor Present Wei ht Wei ht gfigl Remarks Lo s. Condition of Lid Inhibitor Logs, Condition of Lid Gms. Gms.

7 days... Mild weather; contents changed daily 1. 6 Reddish scale, pitting Crotonsldehyde. 0. 845 Black scale. 40 days-.. 5 days, mild weather, avers e max- 1.5 Severe flaking, reddish scale... ....do 0.3 Fairly adherent min temperature 6045; 6 ays exblack scale.

posure to 140 F. obtained by using infra-red lamps; 29 days exposure to 000] early winter weather. Contents changed three times. 10 days. weather, contentschanged every Benzaldehyde... 2. 9 Reddish scale. 10 days-.- any? Formaldehyde 5.1 Do.

The results of the tests show quite conclusively that the low molecular weight alpha, beta-unsaturated aldehydes, particularly crotonaldehyde, effectively inhibit the corrosive effects on metals resulting from exposure to a confined hydrogen sulfide-air-water system. Particular attention is invited to the results shown for the corrosion tests in which the Soxhlet extraction apparatus was used to effect the corrosion conditions. Therein are reported results which show the ineffectiveness of inhibitors which the prior art shows are quite effective in combating the corrosive effects caused by contacting a metal with a hydrogen sulfide-brine-containing system, viz, formaldehyde, isoquiniline. This illustrates quite adequately that one is not able with any accuracy to forecast the behavior of one hydrogen sulfide-containing system from the behavior of another. The peculiarities of said systems of necessity provide the criteria of inhibition for each respective system and an inhibitor of corrosion in one corrosive system may be an accelerator of corrosion in another corrosive system, e. g., formaldehyde.

While not intending to be limited in the application of this invention by any theory of operation, we have found that in order to inhibit the corrosion of metals by hydrogen sulfide-air-water a compound must possess one or both of the following properties:

(1) Capable of adsorption onto a metal surface, thus increasing anodic or cathodic polarization.

(2) Capable of dissolution in water, with subsequent interference with the difiusion of metal ions away from the surface of the metal, or with subsequent interference with difiusion of reactants toward the metal surface.

By virtue of its reactive coniugated double bonds, crotonaldehyde apparently absorbs preferentially onto the cathodic areas of the metal. A covalent type linkage between metal lattice or sulfide ions and conjugated double bond is probably formed. The mode of action seems to be the prevention of oxidation of iron sulfide to free so limited in'extent of operation. Any metal surface in contact with a confined atmosphere containing hydrogen sulfide, air and water is subject to the corrosive effects of said atmosphere and these deleterious effects may be mitigated by applying the teachings of this invention to the particular installation. Installations having such corrosion problems are exemplified by storage tanks" used to store unpurified carbon bisulfide produced from methane and elemental sulfur, or process vessels or storage tanks used in the Claus process for the conversion of hydrogen sulfide to elemental sulfur, which contain the said confined corrosive atmosphere.

It is the intention of this invention to provide a means for protecting any metallic material of construction that is used in the erection of vessels and tanks that are in a service in which the corrosive environment against which our invention provides protection is present. In addition to the conventional structural materials used for the construction of such vessels and tanks such as iron and steel alloys, it is within the scope of our invention to provide protection against corrosion of other structural materials exemplified by the lighter weight metals such as aluminum, magnesium and the like and their alloys.

What is claimed as my invention is:

1. A method of inhibiting the corrosion of metals comprising adding a small proportion of a partially water soluble, low molecular weight alpha, beta-unsaturated aldehyde to a confined, metal-corrosive medium consisting essentially of hydrogen sulfide, air and water.

2. A method of inhibiting the corrosion of ferrous metals subject to corrosion when exposed to a confined, metal corrosive medium consisting essentially of hydrogen sulfide, air and water comprising dispersing in the said corrosive medium a small proportion of a low molecular weight, partially water soluble, alpha, beta-unsaturated aldehyde in the vapor phase.

3. A method of inhibiting the corrosion of structural metals subject to the corrosive action 1 oi a confined, vaporoua'metal-corrosive medium consisting essentially of hydrogen sulfide, air and .water, comprising the introduction in the vapor phase of a low molecular weight partially .water soluble alpha, beta-unsaturated aldehyde into the said corrosive medium.

4. A method in accordance with claim 3 in -which the low molecular weight alpha, beta-un- 6. A method in accordance with claim 5 in which the aldehyde is selected from the group N consisting of crotonaldehyde and acrolein. I

7. Amethod in accordance with cla'im 5 in which the aldehyde iscrotonaldehyde.

8. A method in accordance with claim 5.

GLENN A. mmsni which the aldehyde is acrolein.

REFERENCES CITED The following references are of record in the .file of this patent:

UNITED STATES PATENTS Number Name Date 1,654,229 Wurzschmitt Dec. 27, 1927 1,800,693 Major Apr. 14, 1931 1,983,031 Himebaugh Dec. 4, 1934 2,019,559 Burke Nov. 5, 1935 2,426,318 Menaul Aug. 26, 1947 

1. A METHOD OF INHIBITING THE CORROSION OF METALS COMPRISING ADDING A SMALL PROPORTION OF A PARTIALLY WATER SOLUBLE, LOW MOLECULAR WEIGHT ALPHA, BETA-UNSATURATED ALDEHYDE TO A CONFINED, METAL-CORROSIVE MEDIUM CONSISTING ESSENTIALLY OF HYDROGEN SULFIDE, AIR AND WATER. 